Question 13

College Answer

The cardioverter/defibrillator is usually inserted for ventricular arrhythmias resistant to antiarrhythmics or where antiarrhythmics are contraindicated. The patients usually have severe LV dysfunction and this has its own implications. Batteries usually last for 5-7 years and AV pacing facility is included.

In routine elective surgery its presence should not effect the patient’s management greatly but it may have been switched off because of the interference from diathermy. Cardiac surgery may have displaced a lead or fractured a lead, there is a risk of lead or box infection if bacteraemia occurs and threshold may be changed by medications. It is important to check with the responsible technician and cardiologist for programming and idiosyncrasies of the unit and maintain ECG monitoring with external defibrillator available.

Problems that arise from the device include –

•    Battery depletion

•    Lead fracture or displacement

•    Infection

•    Multiple shocks due to algorithm error, sensing failure, oversensing of physiological signals and lead failure

•    EMF interference from shaver, TV remote, MRI are also possible.

Discussion

Conditions which pose as indications for the insertion of an AICD are more threatening than the AICD itself, in my opinion.

Thus, the device itself affects ICU mangement only insofar as

• it may malfunction, and either fail to pace or fail to shock
• it may function too well (i.e. shock too often)
• it may make imaging and procedures more difficult or impossible (eg. MRI).
• it may act as a nidus for infection.

There is a beautiful and freely available article by Pinski et al which lists not only the common AICD-related problems, but also the solutions to them. In brief, the following problems may be encountered:

Total device failure: there is no pacing or AICD activity. The device appears dead for all intents and purposes. There are several possible causes for this:

• Its battery may run out if it has not been checked recently.
• The surgery may have damaged it, rendering it inoperable.
• The anaesthetist had it turned off, in order to allow safe diathermy, and failed to turn it back on again.
• The patient was externally defibrillated, and a 200J shock has completely fried the AICD circuitry.

Pacing failure: the device seems to be working (pacing spikes are seen on ECG) but there is no capture. This usually means something has happened to its interface with the myocardium.

• The leads have become dislodged, eg. in moving the patient, or in the process of CVC insertion (classically, the PA catheter is to blame)
• The whole device has been dislodged in some way, also pulling out the leads. Classically, this is associated with a demented patient who fiddles with their device.
• The myocardium underlying the pacing lead has infarcted.
• The lead has become infected

Failure to defibrillate VT or VF: the patient is clearly dying but the AICD for some reason refuses to rescue them. Why might that be? It is usually some sort of programing error. For instance:

• Inappropriately high rate cutoff: the VT is not fast enough
• Failure to satisfy multiple detection criteria (too many criteria)
• Completed cycle, exhaustion of therapies (the AICD has run out of ideas)
• Cross-inhibition by separate pacemaker

Overenthusiastic defibrillation: the device is shocking the patient relentlessly.

• There is a genuine VT storm,
• There is electrical interference, eg. from diathermy
• The AICD is suffering a software error and is misinterpreting normal cardiac function or diaphragmatic myopotentials, delivering "spurious" shocks.

Inappropriately normal function: the device missed the family conference, and does not realise the patient is being palliated. In these situations the AICD should be disabled. Ethical issues arise if the patient has an underlying complete heart block or something similar (in which you might want to merely disable the defib function).

Logistic consequences of having an implantable device: i.e. problems with having some implanted object, with or without intrinsic electrical activity.

• it may act as a nidus for infection
• it interferes with line placement
• it makes MRI impossible
• it creates CT artifact, obscuring chest pathology

Obscure problems not unique to AICDs but common to PPMs as well:

• Defib pad positioning for external defibrillation (if the AICD has failed) should be at least 8cm from the device, as per ARC guidelines. External defibrillation may cause device malfunction (Gould, 1981) - though, arguably, if you're using it on an AICD-equipped patient then the device has already malfunctioned.
• Automated external defibrillators, when trying to interpret the rhythm of an arrested patient, may interpret the pacing spikes of a PPM or AICD as QRS complexes (Monsieurs, 1995). The consequences of this would be somebody potentially missing out on a lifesaving shock.
• Demented patients can dislodge or malposition their own pacemaker leads ("Twiddler's syndrome"- Nicholson et al, 2003). 
•  The device may explode in the crematorium, and though this is one of the  "problems may be associated with the device"  to mention this would probably generate no marks in this SAQ as it seems to refer to a living elective post-op patient. It is, however, a serious problem. "In the wall of the cremator was a finger-sized hole half an inch deep", report Gale et al (2002)

A bit of general information about the AICDs: DiMarco, John P. "Implantable cardioverter–defibrillators." New England Journal of Medicine 349.19 (2003): 1836-1847.

A more specific look at the problems they can cause: Pinski, Sergio L. "Emergencies related to implantable cardioverter-defibrillators."Critical care medicine 28.10 (2000): N174-N180.

GOULD, LAWRENCE, et al. "Pacemaker failure following external defibrillation." Pacing and Clinical Electrophysiology4.5 (1981): 575-577.

Gale, Christopher P., and Graham P. Mulley. "Pacemaker explosions in crematoria: problems and possible solutions." Journal of the Royal Society of Medicine 95.7 (2002): 353-355.

Monsieurs, Koenraad G., et al. "Semi-automatic external defibrillation and implanted cardiac pacemakers: understanding the interactions during resuscitation." Resuscitation 30.2 (1995): 127-131.

Nicholson, William J., Kathryn A. Tuohy, and Peter Tilkemeier. "Twiddler's syndrome." New England Journal of Medicine348.17 (2003): 1726-1727.